1. Field of the Invention
The present invention relates generally to an intake air flow rate control system for an internal combustion engine of an automotive vehicle. More specifically, the present invention relates to an automatic electronic intake air flow rate control system in use with a microcomputer for the internal combustion engine of the automotive vehicle, particularly for controlling air flow rate during idling of the engine of the vehicle.
2. Description of the Prior Art
In recent years, pollution of the atmosphere by nitrogen oxides NO.sub.x, carbon monoxide CO, gaseous sulfurous acid and so on produced in the exhaust gas of automotive vehicles has become a serious social problem. In addition to this, the price of fuel, i.e. gasoline or petrol, for automotive vehicles has become higher and higher, because of the limited resources thereof. For preventing atmospheric pollution caused by exhaust gas of vehicles and for improving economic fuel use, it has become necessary to control engine speed accurately even when the vehicle engine is idling.
Further, it has been required to control the engine speed corresponding to various control parameters, such as, kind of transmission, or drive gear neutral position of the transmission on or off condition of the air conditioner and so on by which engine load condition is varied. Particularly during idling condition, since the idle engine speed is relatively slow so as not to drive the engine, the required air flow rate is varied corresponding to engine load. To this end, various control systems have been developed for controlling engine speed corresponding to load applied to engine. Again, the conventional engine speed control systems have been controlling engine speed corresponding to only one or two of engine speed control parameters. Even if it is attempted to combine the conventional control systems that operate with respect to the various control parameters, such combination will be impossible to complete for stabilizing engine speed, because the systems have not been designed to be combinable.
Further, in the conventional systems, either open loop control or the feedback control has been used for controlling the engine speed. However, for controlling the engine speed completely, it is desirable to selectively use both open loop and feedback controls. If feedback contol and open loop control as in the prior art are combined to be selectively applied, there is further required a means for determining whether feedback control can be carried out during particular engine driving conditions. As a further requirement an automatic switching means responsive to either feedback control or open loop control carries out control. However, there have not been developed any control system for effectively switching control operation between open loop and feedback (closed loop) selectively, before the present invention.
Moreover, the conventional control systems have generally employed analog circuitry which have required a considerable amount of electric current. In such systems, control inertia has been quite large so as to cause delay of response with respect to change of control parameters.
In consideration of the above-mentioned disadvantages or inconveniences of the conventional control systems, the present invention provides an engine control method and system, generally for engine idling, which can improve all the defects in the prior arts.